diff --git a/lib/reline/line_editor.rb b/lib/reline/line_editor.rb
index c8b251f78e..577536480e 100644
--- a/lib/reline/line_editor.rb
+++ b/lib/reline/line_editor.rb
@@ -813,23 +813,20 @@ def editing_mode
     @menu_info = MenuInfo.new(list)
   end
 
-  private def filter_normalize_candidates(target, list)
-    target = target.downcase if @config.completion_ignore_case
-    list.select do |item|
-      next unless item
-      unless Encoding.compatible?(target.encoding, item.encoding)
-        # Workaround for Readline test
-        if defined?(::Readline) && ::Readline == ::Reline
+  # Candidates are not filtered by target. Readline (and readline-ext) treats
+  # filtering as completion_proc's responsibility and uses the returned
+  # candidates as-is.
+  private def normalize_candidates(target, list)
+    candidates = list.compact
+    if defined?(::Readline) && ::Readline == ::Reline
+      # Workaround for Readline test
+      candidates.each do |item|
+        unless Encoding.compatible?(target.encoding, item.encoding)
           raise Encoding::CompatibilityError, "incompatible character encodings: #{target.encoding} and #{item.encoding}"
         end
       end
-
-      if @config.completion_ignore_case
-        item.downcase.start_with?(target)
-      else
-        item.start_with?(target)
-      end
-    end.map do |item|
+    end
+    candidates.map do |item|
       item.unicode_normalize
     rescue Encoding::CompatibilityError
       item
@@ -837,7 +834,8 @@ def editing_mode
   end
 
   private def perform_completion(preposing, target, postposing, quote, list)
-    candidates = filter_normalize_candidates(target, list)
+    candidates = normalize_candidates(target, list)
+    return if candidates.empty?
 
     case @completion_state
     when CompletionState::PERFECT_MATCH
@@ -855,7 +853,6 @@ def editing_mode
     end
 
     completed = Reline::Unicode.common_prefix(candidates, ignore_case: @config.completion_ignore_case)
-    return if completed.empty?
 
     append_character = ''
     if candidates.include?(completed)
@@ -873,6 +870,10 @@ def editing_mode
       @completion_state = CompletionState::MENU
       menu(candidates) if @config.show_all_if_ambiguous
     end
+    # Aligned with GNU readline: TAB completion with no common prefix leaves
+    # the line as-is but still displays candidates on the next TAB.
+    return if completed.empty?
+
     @buffer_of_lines[@line_index] = (preposing + completed + append_character + postposing).split("\n")[@line_index] || String.new(encoding: encoding)
     line_to_pointer = (preposing + completed + append_character).split("\n")[@line_index] || String.new(encoding: encoding)
     @byte_pointer = line_to_pointer.bytesize
@@ -908,7 +909,7 @@ def dialog_proc_scope_completion_journey_data
     list = call_completion_proc(preposing, target, postposing, quote)
     return unless list.is_a?(Array)
 
-    candidates = list.select{ |item| item.start_with?(target) }
+    candidates = list.compact
     return if candidates.empty?
 
     pre = preposing.split("\n", -1).last || ''
@@ -1784,7 +1785,7 @@ def finish
       pre, target, post, quote = retrieve_completion_block
       result = call_completion_proc(pre, target, post, quote)
       if result.is_a?(Array)
-        candidates = filter_normalize_candidates(target, result)
+        candidates = normalize_candidates(target, result)
         menu(candidates)
       end
     end
diff --git a/test/reline/helper.rb b/test/reline/helper.rb
index 6f470a617f..ad69760f7a 100644
--- a/test/reline/helper.rb
+++ b/test/reline/helper.rb
@@ -112,6 +112,17 @@ def input_keys(input)
     end
   end
 
+  # Readline-compatible completion_proc: prefix-filtering candidates is
+  # completion_proc's responsibility, not Reline's.
+  def set_completion_candidates(candidates, ignore_case: false)
+    @line_editor.completion_proc = proc { |word|
+      word = word.downcase if ignore_case
+      candidates.select { |s|
+        (ignore_case ? s.downcase : s).start_with?(word)
+      }.map { |s| convert_str(s) }
+    }
+  end
+
   def set_line_around_cursor(before, after)
     input_keys("\C-a\C-k")
     input_keys(after)
diff --git a/test/reline/test_key_actor_emacs.rb b/test/reline/test_key_actor_emacs.rb
index 7c1dfd0189..52dd67430c 100644
--- a/test/reline/test_key_actor_emacs.rb
+++ b/test/reline/test_key_actor_emacs.rb
@@ -740,16 +740,7 @@ def test_em_upper_case_with_complex_example
   end
 
   def test_em_delete_or_list
-    @line_editor.completion_proc = proc { |word|
-      %w{
-        foo_foo
-        foo_bar
-        foo_baz
-        qux
-      }.map { |i|
-        i.encode(@encoding)
-      }
-    }
+    set_completion_candidates(%w[foo_foo foo_bar foo_baz qux])
     input_keys('fooo')
     assert_line_around_cursor('fooo', '')
     assert_equal(nil, @line_editor.instance_variable_get(:@menu_info))
@@ -765,15 +756,7 @@ def test_em_delete_or_list
   end
 
   def test_completion_duplicated_list
-    @line_editor.completion_proc = proc { |word|
-      %w{
-        foo_foo
-        foo_foo
-        foo_bar
-      }.map { |i|
-        i.encode(@encoding)
-      }
-    }
+    set_completion_candidates(%w[foo_foo foo_foo foo_bar])
     input_keys('foo_')
     assert_line_around_cursor('foo_', '')
     assert_equal(nil, @line_editor.instance_variable_get(:@menu_info))
@@ -786,16 +769,7 @@ def test_completion_duplicated_list
   end
 
   def test_completion
-    @line_editor.completion_proc = proc { |word|
-      %w{
-        foo_foo
-        foo_bar
-        foo_baz
-        qux
-      }.map { |i|
-        i.encode(@encoding)
-      }
-    }
+    set_completion_candidates(%w[foo_foo foo_bar foo_baz qux])
     input_keys('fo')
     assert_line_around_cursor('fo', '')
     assert_equal(nil, @line_editor.instance_variable_get(:@menu_info))
@@ -829,15 +803,7 @@ def test_completion
 
   def test_autocompletion
     @config.autocompletion = true
-    @line_editor.completion_proc = proc { |word|
-      %w{
-        Readline
-        Regexp
-        RegexpError
-      }.map { |i|
-        i.encode(@encoding)
-      }
-    }
+    set_completion_candidates(%w[Readline Regexp RegexpError])
     input_keys('Re')
     assert_line_around_cursor('Re', '')
     input_keys("\C-i")
@@ -857,16 +823,7 @@ def test_autocompletion
   end
 
   def test_completion_with_indent
-    @line_editor.completion_proc = proc { |word|
-      %w{
-        foo_foo
-        foo_bar
-        foo_baz
-        qux
-      }.map { |i|
-        i.encode(@encoding)
-      }
-    }
+    set_completion_candidates(%w[foo_foo foo_bar foo_baz qux])
     input_keys('  fo')
     assert_line_around_cursor('  fo', '')
     assert_equal(nil, @line_editor.instance_variable_get(:@menu_info))
@@ -879,14 +836,7 @@ def test_completion_with_indent
   end
 
   def test_completion_with_perfect_match
-    @line_editor.completion_proc = proc { |word|
-      %w{
-        foo
-        foo_bar
-      }.map { |i|
-        i.encode(@encoding)
-      }
-    }
+    set_completion_candidates(%w[foo foo_bar])
     matched = nil
     @line_editor.dig_perfect_match_proc = proc { |m|
       matched = m
@@ -943,9 +893,7 @@ def test_continuous_completion_disabled_with_perfect_match
   end
 
   def test_completion_append_character
-    @line_editor.completion_proc = proc { |word|
-      %w[foo_ foo_foo foo_bar].select { |s| s.start_with? word }
-    }
+    set_completion_candidates(%w[foo_ foo_foo foo_bar])
     @line_editor.completion_append_character = 'X'
     input_keys('f')
     input_keys("\C-i")
@@ -959,9 +907,7 @@ def test_completion_append_character
   end
 
   def test_completion_with_quote_append
-    @line_editor.completion_proc = proc { |word|
-      %w[foo bar baz].select { |s| s.start_with? word }
-    }
+    set_completion_candidates(%w[foo bar baz])
     set_line_around_cursor('x = "b', '')
     input_keys("\C-i")
     assert_line_around_cursor('x = "ba', '')
@@ -983,29 +929,22 @@ def test_completion_with_quote_append
   end
 
   def test_completion_with_completion_ignore_case
-    @line_editor.completion_proc = proc { |word|
-      %w{
-        foo_foo
-        foo_bar
-        Foo_baz
-        qux
-      }.map { |i|
-        i.encode(@encoding)
-      }
-    }
+    set_completion_candidates(%w[foo_foo foo_bar Foo_baz qux], ignore_case: true)
     input_keys('fo')
     assert_line_around_cursor('fo', '')
     assert_equal(nil, @line_editor.instance_variable_get(:@menu_info))
     input_keys("\C-i")
-    assert_line_around_cursor('foo_', '')
+    # completion_ignore_case is false: the candidates have no common prefix
+    assert_line_around_cursor('fo', '')
     assert_equal(nil, @line_editor.instance_variable_get(:@menu_info))
     input_keys("\C-i")
-    assert_line_around_cursor('foo_', '')
-    assert_equal(%w{foo_foo foo_bar}, @line_editor.instance_variable_get(:@menu_info).list)
+    assert_line_around_cursor('fo', '')
+    assert_equal(%w{foo_foo foo_bar Foo_baz}, @line_editor.instance_variable_get(:@menu_info).list)
     @config.completion_ignore_case = true
+    input_keys('o')
     input_keys("\C-i")
+    # completion_ignore_case affects the common prefix computation
     assert_line_around_cursor('foo_', '')
-    assert_equal(%w{foo_foo foo_bar Foo_baz}, @line_editor.instance_variable_get(:@menu_info).list)
     input_keys('a')
     input_keys("\C-i")
     assert_line_around_cursor('foo_a', '')
@@ -1018,17 +957,29 @@ def test_completion_with_completion_ignore_case
     assert_line_around_cursor('Foo_baz', '')
   end
 
+  # Readline never filters candidates by the input word. Filtering is
+  # completion_proc's responsibility.
+  def test_completion_does_not_filter_candidates
+    @line_editor.completion_proc = proc { |word| %w{ABCX abcy} }
+    input_keys('z')
+    input_keys("\C-i")
+    assert_line_around_cursor('z', '')
+    assert_equal(nil, @line_editor.instance_variable_get(:@menu_info))
+    input_keys("\C-i")
+    assert_line_around_cursor('z', '')
+    assert_equal(%w{ABCX abcy}, @line_editor.instance_variable_get(:@menu_info).list)
+  end
+
+  def test_completion_replaces_word_with_ignore_case_common_prefix
+    @config.completion_ignore_case = true
+    @line_editor.completion_proc = proc { |word| %w{ABCX abcy} }
+    input_keys('z')
+    input_keys("\C-i")
+    assert_line_around_cursor('ABC', '')
+  end
+
   def test_completion_in_middle_of_line
-    @line_editor.completion_proc = proc { |word|
-      %w{
-        foo_foo
-        foo_bar
-        foo_baz
-        qux
-      }.map { |i|
-        i.encode(@encoding)
-      }
-    }
+    set_completion_candidates(%w[foo_foo foo_bar foo_baz qux])
     input_keys('abcde fo ABCDE')
     assert_line_around_cursor('abcde fo ABCDE', '')
     input_keys("\C-b" * 6 + "\C-i")
@@ -1044,6 +995,8 @@ def test_completion_with_nil_value
         foo_bar
         Foo_baz
         qux
+      }.select { |s|
+        s.downcase.start_with?(word.downcase)
       }.map { |i|
         i.encode(@encoding)
       }.prepend(nil)
diff --git a/test/reline/test_key_actor_vi.rb b/test/reline/test_key_actor_vi.rb
index 083433f9a8..253545adad 100644
--- a/test/reline/test_key_actor_vi.rb
+++ b/test/reline/test_key_actor_vi.rb
@@ -562,14 +562,7 @@ def test_vi_list_or_eof_with_non_empty_line
   end
 
   def test_completion_journey
-    @line_editor.completion_proc = proc { |word|
-      %w{
-        foo_bar
-        foo_bar_baz
-      }.map { |i|
-        i.encode(@encoding)
-      }
-    }
+    set_completion_candidates(%w[foo_bar foo_bar_baz])
     input_keys('foo')
     assert_line_around_cursor('foo', '')
     input_keys("\C-n")
@@ -587,14 +580,7 @@ def test_completion_journey
   end
 
   def test_completion_journey_reverse
-    @line_editor.completion_proc = proc { |word|
-      %w{
-        foo_bar
-        foo_bar_baz
-      }.map { |i|
-        i.encode(@encoding)
-      }
-    }
+    set_completion_candidates(%w[foo_bar foo_bar_baz])
     input_keys('foo')
     assert_line_around_cursor('foo', '')
     input_keys("\C-p")
@@ -612,14 +598,7 @@ def test_completion_journey_reverse
   end
 
   def test_completion_journey_in_middle_of_line
-    @line_editor.completion_proc = proc { |word|
-      %w{
-        foo_bar
-        foo_bar_baz
-      }.map { |i|
-        i.encode(@encoding)
-      }
-    }
+    set_completion_candidates(%w[foo_bar foo_bar_baz])
     input_keys('abcde fo ABCDE')
     assert_line_around_cursor('abcde fo ABCDE', '')
     input_keys("\C-[" + 'h' * 5 + "i\C-n")
@@ -639,14 +618,7 @@ def test_completion_journey_in_middle_of_line
   end
 
   def test_completion
-    @line_editor.completion_proc = proc { |word|
-      %w{
-        foo_bar
-        foo_bar_baz
-      }.map { |i|
-        i.encode(@encoding)
-      }
-    }
+    set_completion_candidates(%w[foo_bar foo_bar_baz])
     input_keys('foo')
     assert_line_around_cursor('foo', '')
     input_keys("\C-i")
@@ -655,15 +627,7 @@ def test_completion
 
   def test_autocompletion_with_upward_navigation
     @config.autocompletion = true
-    @line_editor.completion_proc = proc { |word|
-      %w{
-        Readline
-        Regexp
-        RegexpError
-      }.map { |i|
-        i.encode(@encoding)
-      }
-    }
+    set_completion_candidates(%w[Readline Regexp RegexpError])
     input_keys('Re')
     assert_line_around_cursor('Re', '')
     input_keys("\C-i")
@@ -678,15 +642,7 @@ def test_autocompletion_with_upward_navigation
 
   def test_autocompletion_with_upward_navigation_and_menu_complete_backward
     @config.autocompletion = true
-    @line_editor.completion_proc = proc { |word|
-      %w{
-        Readline
-        Regexp
-        RegexpError
-      }.map { |i|
-        i.encode(@encoding)
-      }
-    }
+    set_completion_candidates(%w[Readline Regexp RegexpError])
     input_keys('Re')
     assert_line_around_cursor('Re', '')
     input_keys("\C-i")
@@ -701,14 +657,7 @@ def test_autocompletion_with_upward_navigation_and_menu_complete_backward
 
   def test_completion_with_disable_completion
     @config.disable_completion = true
-    @line_editor.completion_proc = proc { |word|
-      %w{
-        foo_bar
-        foo_bar_baz
-      }.map { |i|
-        i.encode(@encoding)
-      }
-    }
+    set_completion_candidates(%w[foo_bar foo_bar_baz])
     input_keys('foo')
     assert_line_around_cursor('foo', '')
     input_keys("\C-i")